3-amino-2,5-dichlorobenzoic acid and its alkali metal salts are well known in the art as important selective herbicides. The herbicidal activity of 3-amino-2,5-dichlorobenzoic acid, its functional derivatives and their preparation from the 3-nitro compounds are described in U.S. Pat. Nos. 3,014,063 and 3,174,841. The alkali metal salt is preferred since it is a water-soluble form of 3-amino-2,5-dichlorobenzoic acid which can be produced as a dry powder, thereby permitting reduction in packaging and shipping costs. It is known that the alkali metal salt of 3-amino-2,5-dichlorobenzoic acid can be prepared by reacting 3-amino-2,5-dichlorobenzoic acid with alkali metal base, or by reacting the amine salt of the acid (which cannot easily be produced free of water) with sodium hydroxide and removing the liberated amine from solution.
It is also known that the sodium salt of 3-amino-2,5-dichlorobenzoic acid can be prepared by the reduction of the sodium salt of 3-amino-2,5-dichlorobenzoic acid with hydrogen in the presence of Raney nickel catalyst. By way of illustration, such a reduction is described in U.S. Pat. No. 3,910,995.
The reduction process described in the above patent provides the sodium salt of 3-amino-2,5-dichlorobenzoic acid in relatively low yield. Consequently, there exists a need for more effective process for preparing the alkali metal salt of 3-amino-2,5-dichlorobenzoic acid in increased yield that avoids the need to resort to elaborate and cumbersome purification techniques.